The purpose of this study was to examine the relationship between reflection performance and the learning effect with learners in a web-based portfolio assessment environment. The participants were 45 eighth graders randomly selected from computer classes at a middle school in Taiwan. The reflection performance in this study included frequency of reviewing peers' reflections, time spent reading peers' reflections, and grades awarded for those reflections, whereas the learning effect included the project, test, and attitude. The data collection was conducted through an online portfolio assessment (including reflection, project, and attitude) and a final test. The results by Pearson's correlation approach revealed that (a) the frequency of reviewing peers' reflections was significantly and positively related with attitude; (b) the time spent reading peers' reflections was significantly and positively related with project and attitude; and (c) the grade awarded for reflection was significantly and positively correlated with project and attitude. Overall, among the three aspects of learning effect, attitude had the strongest relationship with reflection performance, followed by project and test.